1. Field of the Invention
The present invention relates to an X-ray generating apparatus for generating an X-ray by bombarding an anode target with an electron emitted from a cathode, an X-ray imaging apparatus for capturing an X-ray transmission image formed upon irradiating an object to be inspected with the X-ray generated by the X-ray generating apparatus, and an X-ray inspection system for inspecting the object to be inspected being transferred in a predetermined direction with an X-ray.
2. Related Background Art
Conventionally known as an X-ray generating apparatus having an X-ray tube for generating an X-ray by bombarding an anode target with an electron emitted from a cathode is one disclosed in U.S. Pat. No. 5,077,771. The X-ray generating apparatus disclosed in this publication uses a PWM system as a method of controlling the grid voltage applied to a grid electrode, so as to regulate the effective grid voltage by changing the pulse width of control pulses.
Typical inspecting apparatus often use a technique which captures an image (still image) of an object to be inspected by flashing (pulsing) a light source. While such a technique has been desired to be applied to X-ray inspections as well, examples realizing an X-ray generating apparatus adapted to pulse an X-ray generated from an X-ray tube have hardly been known. In an X-ray tube, the X-ray output generated therein will change greatly even if the voltage applied to each electrode changes only slightly. Therefore, stable pulsing X-rays are hard to generate, and a technique for generating stable pulsing X-rays has not fully be established yet.
In view of the points mentioned above, it is a first object of the present invention to provide an X-ray generating apparatus which can generate a stable pulsing X-ray from an X-ray tube.
It is a second object of the present invention to provide an X-ray imaging apparatus which can accurately acquire an X-ray transmission image formed upon irradiating an object to be inspected with a stable pulsing X-ray generated from an X-ray tube.
It is a third object of the present invention to provide an X-ray inspecting system which can irradiate an object to be inspected being transferred in a predetermined direction with a stable pulsing X-ray generated from an X-ray tube, thereby being able to accurately acquire an X-ray transmission image of the object formed upon irradiation with the stable pulsing X-ray.
For achieving the first object, the X-ray generating apparatus of the present invention comprises an X-ray tube for generating, within a housing sealed into vacuum, an X-ray by focusing an electron emitted from a cathode into an anode target by way of a first grid electrode, a second grid electrode, and a focusing electrode; grid voltage control means for controlling a grid voltage applied to the first grid electrode; and pulse generating means for generating a pulse which changes from an OFF state to an ON state and keeps the ON state for a predetermined period of time; wherein the grid voltage control means applies, in response to the pulse generated by the pulse generating means, a cutoff voltage to the first grid electrode when the pulse is in the OFF state so as to prevent the electron emitted from the cathode from reaching the anode target, and applies to the first grid electrode, in response to the pulse generated by the pulse generating means, a grid operating voltage adjusted such that the electron emitted from the cathode so as to bombard the anode target attains a predetermined amount of quantity when the pulse is in the ON state.
In response to the pulse generated by the pulse generating means, the grid voltage control means applies a cutoff voltage to the first grid electrode when the pulse is in the OFF state so as to prevent the electron emitted from the cathode from reaching the anode target, and applies to the first grid electrode a grid operating voltage adjusted such that the electron emitted from the cathode so as to bombard the anode target attains a predetermined value of quantity. As a consequence, the X-ray tube can generate a pulsing X-ray having a pulse width corresponding to the period during which the grid operating voltage is applied to the first grid electrode. Also, since the grid operating voltage applied to the first grid electrode is adjusted such that the electron emitted from the cathode so as to bombard the anode target attains a predetermined value of quantity, the pulsing X-ray generated from the X-ray tube can be stabilized.
The X-ray generating apparatus of the present invention may be characterized in that the grid voltage control means has cathode current detecting means for detecting a cathode current and, in response to the pulse generated by the pulse generating means, applies to the first grid electrode a grid operating voltage adjusted such that the cathode current detected by the cathode current detecting means attains a predetermined value when the pulse is in the ON state.
While the cathode current detecting means detects the cathode current, the grid voltage control means applies to the first grid electrode the grid operating voltage adjusted such that the cathode current attains a predetermined value. For example, means for detecting the anode target current may be provided as means for detecting the quantity of electron emitted to the cathode so as to bombard the anode target. However, a high voltage is usually applied to the anode target, whereby the anode target current is hard to detect. Hence, the cathode current detecting means can easily detect the quantity of the electron emitted from the cathode so as to bombard the anode target, whereby the grid voltage control means can easily adjust the grid operating voltage.
The X-ray generating apparatus of the present invention may be characterized in that the cathode current detecting means has a cathode current detecting resistor, connected to the cathode, for detecting the cathode current; and that the grid voltage control means has a negative voltage generating section for generating a predetermined negative voltage; a pulse inverter for inputting the pulse generated by the pulse generating means and generating an inverted pulse in which the ON and OFF states of the inputted pulse are inverted; a first switch for inputting the inverted pulse generated by the pulse inverter and outputting the predetermined negative voltage generated by the negative voltage generating section when the inverted pulse is in the ON state; a reference voltage generating section for generating a reference positive voltage; a second switch for inputting the pulse generated by the pulse generating means and outputting, when the pulse is in the ON state, the reference positive voltage generated by the reference voltage generating section; an operational amplifier having one input terminal for inputting a voltage generated by the cathode current detecting resistor and the other input terminal for inputting the predetermined negative voltage outputted from the first switch and the reference positive voltage outputted from the second switch; and a grid voltage control circuit for controlling, in response to an output from the operational amplifier, the grid voltage applied to the first grid electrode.
The configuration of the grid voltage control means for controlling the grid voltage applied to the first grid electrode in order to generate a stable pulsing X-ray can be realized by a simple, low-cost circuit configuration.
For achieving the second object, the X-ray imaging apparatus of the present invention comprises imaging means for capturing an X-ray transmission image formed upon irradiating an object to be inspected with the X-ray generated by the X-ray generating apparatus according to claim 1; wherein the imaging means receives the pulse generated by the pulse generating means and captures the X-ray transmission image when the pulse is in the ON state.
The imaging means receives the pulse generated by the pulse generating means, and captures the X-ray transmission image when the pulse is in the ON state. As a consequence, the imaging means can accurately acquire the X-ray transmission image formed upon irradiating the object to be inspected with the stable pulsing X-ray generated from the X-ray tube.
For achieving the third object, the X-ray inspection system of the present invention comprises the X-ray generating apparatus according to claim 1, an X-ray imaging apparatus having imaging means for capturing an X-ray transmission image formed upon irradiating an object to be inspected with an X-ray generated by the X-ray generating apparatus; and object detecting means for detecting arrival of the object in an imaging area in the X-ray imaging apparatus; wherein the pulse generating means has trigger signal outputting means for outputting a trigger signal according to the detection of the object by the object detecting means and outputs the pulse when the trigger signal is outputted from the trigger signal outputting means; and wherein the imaging means receives the pulse outputted from the pulse generating means and captures the X-ray transmission image when the pulse is in the ON state.
The arrival of the object to be inspected in the imaging area in the X-ray imaging apparatus is detected by the object detecting means and, according to the detection, the trigger signal generating means generates a trigger signal, and the pulse generating means generates a pulse. As a consequence, when the pulse is in the ON state, a stable pulsing X-ray is generated from the X-ray tube. In response to the pulse generated by the pulse generating means, the imaging means captures the X-ray transmission image when the pulse is in the ON state. Therefore, the object to be inspected being transferred in a predetermined direction can be irradiated with a stable pulsing X-ray, whereby the X-ray transmission image of the object formed upon irradiation with the stable pulsing X-ray can be acquired accurately.
For achieving the first object, the X-ray generating apparatus of the present invention comprises an X-ray tube having a cathode, an anode target, and a first grid electrode, a second grid electrode, and a focusing electrode which are disposed between the cathode and the anode target; and grid voltage control means for controlling a grid voltage applied to the first grid electrode such that a pulsing X-ray having a predetermined pulse width is generated from the X-ray tube.
The grid voltage control means controls the grid voltage applied to the first grid electrode such that a pulsing X-ray having a predetermined pulse width is generated from the ray tube. As a consequence, a pulsing X-ray having a predetermined pulse width can be generated from the X-ray tube.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.